VI PREFACE. 



The author may have fallen on the rocks of Scylla 

 in an attempt to change the character of a monograph, 

 which must necessarily take something of an abstruse 

 shape. He is sensible of many short-comings. A per- 

 formance is mostly very different from an ideal. 



None more feelingly than the investigator of natural 

 law will echo the poet's words : — 



"In seeking to undo 



One riddle and to find the trne, 

 I knit a hundi'ed others new." 



